Previous years of this project have focussed on determining the conditions for maintenance and inducibility of cytochrome P450 in chick hepatocyte in tissue culture. Cytochromes P450 are a class of hemoproteins which are responsible for activation of most carcinogens, the liver being most active in this activation. In this proposal we will extend our studies to characterize the total species of P450's and the Phase II enzyme uridine diphosphoglucuronyl transferase induced by several chemical treatments. The basis relationships between heme metabolism and cytochrome P450 inductions will be investigated in the chick lever culture. We will investigate whether the lower inducibility of P450 in rat liver cell cultures by many of these chemicals may be due to culture-induced changes in heme metabolism or to an inapparopriate extracellular matrix. The protential usefulness of the chick liver culture for carcinogen activation studies will be tested by a) metabolic studies of benz(a)pyrene and acetylaminofluorene, b) carcinogen-mediated mutagenesis in Chinese hamster V79 cells in co-culture with chick liver cells induced for different species of cytochrome P450 and c) DNA lesions produced by chromate and the parallel decrease in inducible enzyme activities.